Recently, a piezoelectric actuator is attracting attention in the field of portable information equipment, chemical industry and medical field as a novel motor in place for an electromagnetic motor, as it can achieve a miniaturization and a high density in motors. Also the piezoelectric actuator in its drive does not generate electromagnetic noises nor is affected by noises. Furthermore, the piezoelectric actuator is attracting attention as a technology for producing an equipment of submillimeter dimension as represented by a micromachine, and a small piezoelectric actuator is desired as a drive source for such micromachines.
A prior piezoelectric element is generally composed of a piezoelectric member, formed by working a bulk sintered member and provided in a predetermined position on a substrate such as of a metal or silicon. The piezoelectric member is obtained by polishing a bulk sintered member into desired size and thickness, or obtained by punching from a green sheet, followed by a heat treatment. Such bulk sintered member or a molded member from the green sheet generally has a thickness of several micrometers or larger. Such piezoelectric actuator generally has a basic structure in which a piezoelectric member and an elastic material are adhered with an adhesive material.
On the other hand, in addition to the adhesion with the adhesive material, there is known a method of forming a piezoelectric member directly on a substrate for example by sputtering or printing method. Usually the piezoelectric member formed by a printing method, a sputtering method, an MOCVD method, a sol-gel method or a gas deposition method has a thickness of about several tens of nanometers (several hundred Angstroms) to several hundred micrometers. Also in either structure, the piezoelectric member is provided with electrodes through which a voltage is applied.
As explained in the foregoing, the piezoelectric element basically has a structure in which a piezoelectric element and a substrate are adhered with an adhesive material, or a structure in which a piezoelectric member is directly formed on a substrate.
An ink jet recording apparatus utilizing such piezoelectric element is formed by a pressure chamber communicating with an ink supply chamber, and an ink discharge port communicating with the pressure chamber, wherein such pressure chamber is provided with a vibrating plate on which a piezoelectric element is adjoined or directly formed. In such configuration, a predetermined voltage is applied to the piezoelectric element to cause an elongation or a contraction therein, thereby inducing a bending vibration to compress ink in the pressure chamber and to discharge a droplet of ink liquid from the ink discharge port. Such function is currently utilized in a color ink jet recording apparatus, but there is being desired an improvement in the printing performance, particularly a higher resolution and a higher printing speed. For this purpose, there is being tried a multi nozzle head structure with a miniaturized ink jet head structure for achieving a higher resolution and a higher printing speed. For miniaturizing an ink jet head, it is necessary to compactize a piezoelectric element for discharging the ink.
Such compact piezoelectric element has been produced by a fine structuring of a sintered piezoelectric member for example by cutting and polishing as explained above, but, there is also being investigated to produce an ultra compact piezoelectric element of a high precision by forming the piezoelectric member as a thin film and utilizing a fine working technology developed in the semiconductor industry. Also for achieving a higher performance, the piezoelectric member is preferably formed by a single crystal film or a single oriented film, and a hetero epitaxial growing technology is being actively developed.
On the other hand, a ferroelectric material of perovskite structure, represented by a general formula ABO3, is recently attracting attention as a piezoelectric material. Such material, as represented by PZT, is excellent in a ferroelectric property, a pyroelectric property and a piezoelectric property. Also a relaxer type electrostrictive material represented by PZN-PT is expected as a piezoelectric material because of its excellent piezoelectric property. The PZT material is explained for example in “Ceramic Yudentai Kogaku” (Gakken-sha, 4th edition), p. 333. Also the relaxer material is described for example in Japanese Patent Application Laid-open No. 2001-328867.
However, it has been found out that even the material having the aforementioned high piezoelectric property cannot realize the piezoelectric property of the expected high level, and that even the piezoelectric and/or electrostrictive material which has an orientation property or is formed by a single crystal and for which a higher piezoelectric property is expected only gives rise, by a mere increase in the crystallinity, to a piezoelectric property not different from that in a piezoelectric and/or electrostrictive material which does not have an orientation property or is not formed by a single crystal. Also there has not been established a piezoelectric element capable of avoiding an electrode peeling of the piezoelectric element, principally resulting from a large piezoelectric strain and encountered when the piezoelectric property is increased, or a film peeling encountered in case of direct formation of the piezoelectric element on the substrate.